Clearly they can be faulty. OP is an example of that. The doctor would take blood work, which is obviously more accurate, showing hormones in the blood. But she has no reason if she's not pregnant . Her mom needs to relax.

They canal would prove or disprove sexual activity the hymen is not the sole indicator. How do you think rape kits work, everyone knows they can even tell how long it has been based on healing. Don't you all watch Law and Order?